date←•Import "datetime.bqn"

F←{𝕊y:
 t0←date.From y‿1‿1‿0‿0‿0
 dow←1-˜•BQN ¯1↓1⊑•SH "date"‿"-d"‿((•Fmt y)∾"-01-01")‿"+%u"
 ((∨´5≤·≠¨(⊑¨)⊸⊔)¨/↕∘≠)1↓(2⊸⊑¨)⊸⊔(4≤⊑¨)⊸/((7|⊢)∾¨(date.To¨(×´24‿60‿60)×⊢))(dow+↕366)
}
⍉⌽F¨⊸≍(⊑+↕∘(1⊸+)∘|∘-´)1900‿2019